Hitherto, in an outdoor unit for an air-conditioning apparatus, a heat exchanger and a blower are accommodated in a casing, and outside air is supplied to the heat exchanger, to thereby exchange heat between the outside air and refrigerant of a refrigeration cycle. When this heat exchanger is to be accommodated in the casing, mounting bases for the heat exchanger are formed on a bottom plate of the casing at a plurality of positions to protrude upward therefrom, and a lower surface of the heat exchanger is mounted on the mounting bases (see, for example, Patent Literature 1).